Centrifugal Compressor

ABSTRACT

A centrifugal compressor is provided. The centrifugal compressor includes a housing and a rotatable assembly mounted for rotation about an axis within the housing. The rotatable assembly includes an impeller forming part of a compressor stage and a motor rotor forming an armature of a motor for driving the rotating assembly about the axis. A first air intake is located at a first end of the apparatus, the first air intake providing an air source for the compressor stage and a second air intake is located at a second end of the apparatus, the second air intake providing an air source for at least two air cooling passageways.

Priority is claimed to U.S. provisional patent application Ser. No. 61/462,801, filed Feb. 7, 2011, entitled “Centrifugal Compressor,” which is referred to and incorporated herein in its entirety by this reference.

FIELD OF THE INVENTION

The present invention generally relates to compressors. More particularly, the invention concerns a centrifugal compressor.

BACKGROUND OF THE INVENTION

Centrifugal compressors have existed for many years, and there exist many different designs. Historically, compressed air (or a gas/air mixture) has been generated by various types of motor driven machines. To achieve high efficiency the motor must drive the centrifugal compressor at high rotational speeds. As rotational speeds become greater the overall machine size can be made smaller, while maintaining the same compressed air flows, pressures, and motor power. However, requirements for running at high speeds include properly designed rotating and non-rotating assemblies and bearings to support the high speed rotating shaft, typically ranging from 30,000 rpm to 200,000 rpm.

Air or water cooling may be employed to dissipate heat that is generated. However, liquid cooling has several drawbacks including additional system complexity and increased manufacturing and unit cost, and the potential for fluid leaks into the compressor/motor internals is also a concern. For the very small machines, power density is exceptional and therefore the ability to reject heat from the machines relatively little surface area becomes challenging.

Therefore, there remains a need to overcome one or more of the limitations in the above-described, existing art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 comprises a perspective view of one embodiment of the centrifugal compressor of the present invention;

FIG. 2 comprises a cross-sectional view of the embodiment of FIG. 1;

FIG. 3 comprises a perspective view of a finned heat exchange element included in the embodiment of FIG. 1;

FIG. 4 comprises a cross-sectional view showing the internal air passageways located within the embodiment of FIG. 1;

FIG. 5 comprises a perspective view of a second embodiment of the centrifugal compressor of the present invention, the second embodiment comprising a fluid-cooled centrifugal compressor; and

FIG. 6 comprises a cross-sectional view of the embodiment of FIG. 5.

It will be recognized that some or all of the Figures are schematic representations for purposes of illustration and do not necessarily depict the actual relative sizes or locations of the elements shown. The Figures are provided for the purpose of illustrating one or more embodiments of the invention with the explicit understanding that they will not be used to limit the scope or the meaning of the claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the centrifugal compressor of the present invention. It will be apparent, however, to one skilled in the art that the centrifugal compressor may be practiced without some of these specific details. Throughout this description, the embodiments and examples shown should be considered as exemplars, rather than as limitations on the centrifugal compressor. That is, the following description provides examples, and the accompanying drawings show various examples for the purposes of illustration. However, these examples should not be construed in a limiting sense as they are merely intended to provide examples of the centrifugal compressor rather than to provide an exhaustive list of all possible implementations of the centrifugal compressor.

Referring now to FIGS. 1-6, the centrifugal compressor 10 includes many novel features including, among others, an air-cooled design that provides reduced system complexity and cost and that also eliminates the possibility of fluid internal leaks into the motor/compressor internals. The air cooled design comprises multiple air-cooling circuits that ensure sufficient cooling air supply for the unit.

Another feature is a foil air bearing system that supports the impeller shaft. The foils eliminate the need for costly high-temperature coatings on the foil bearing surfaces, which are usually required on units that operate at higher operating temperatures.

Yet another feature comprises a heat exchanging element that efficiently transfers heat generated by the electric motor stator and also allows cool air flow passage, thereby dissipating the generated heat.

Other features include a compact, lightweight design that eliminates many seals, gaskets and other elements found in conventional compressors. Yet, the pneumatic power i.e., flow and pressure rise (aka “process air”) equals the output of much larger and heavier units, thereby enabling the installation of the centrifugal compressor 10 in aircraft to provide on-board inert gas and on-board oxygen generation (aka OBIGGS & OBOGS). In at least one exemplary case, a 20 horsepower compressor is attained in a package weight totaling 12 pounds.

As a background, the specific speed of the centrifugal machine is of primary importance to the designer as it relates and balances the general size, i.e., impeller diameter against the rotational speed for a given head rise. For example, impeller diameter may be traded for rotational speed to yield the same head rise. However, there is a limit as to how big a diameter may be traded for reduced rotational speed, without incurring significant losses. For designs that require relatively high pressure rise at relatively low flows, a smaller, faster rotating machine is desired in order to yield an acceptable specific speed.

Referring now to FIGS. 1-2, the centrifugal compressor 10 is illustrated. A first end of the centrifugal compressor 10 comprises the centrifugal compressor axial air inlet 15, with the other, second end comprising the main cooling air inlet 20.

The volute 25 couples to the base housing 30 through the back plate assembly 35 and V-band clamp 40. The base housing 30 includes a heat exchange element 45 (shown in FIG. 3) comprising a plurality of fin elements 50 densely arranged to allow air to pass between the fins along the main axis 55 of the base housing 30.

As shown in FIG. 2, the main cooling air inlet 20 attaches to a fan cover 60 that fits over the rear cover 65, which provides a thrust bearing surface 70 for the impeller shaft assembly, or rotatable assembly 75 that rides on two air bearing journals 80.

Referring again to FIGS. 1-2, the centrifugal compressor 10 is generally symmetric about the compressor axis 55. The compressor inlet 15 receives a fluid medium, generally air, to be compressed, which is discharged as compressed fluid at volute exit 85. The inlet leads to a single centrifugal compressor stage comprised of an impeller 90 with the volute 25 surrounding the impeller 90 and the inlet 15.

As shown in FIG. 2 the rotating assembly, or impeller assembly 75 includes the impeller 90, a shaft 92, a first air bearing journal 80, a permanent magnet motor rotor 95, and second air bearing journal 80, a thrust load bearing 100 that balances the pressure load of the impeller 90. The impeller assembly 75 also includes a fan 105 located at the distal end of the impeller assembly 75, the fan 105 located within the cooling air inlet 15.

The motor rotor 95 in the rotating assembly 75 forms the armature of a electrically driven permanent magnet, high speed motor in which the stator 110 is fixedly retained within the finned heat exchanger 45, as shown in FIG. 2. The motor rotor 95 includes a permanent magnet for enabling operation of the electric motor.

The rotating assembly 75 consisting of the impeller 90, the thrust load balancing disk 100 and the rotor motor 95 are supported for high speed rotation within the housing by means of oil-less air bearings (not shown) that are located between the rotating assembly shaft 92 and the air bearing journals 80. The foil air bearings have numerous performance, maintenance and contamination-free advantages over conventional roller or ball bearings.

Specifically, once the rotating assembly 75 is spinning quickly enough, the working fluid (usually air) pushes the foil away from the shaft 92 so that there is no more contact. The shaft 92 and foil are separated by the air's high pressure which is generated by the rotation which pulls gas into the bearing via viscosity effects. A high speed of the shaft 92 with respect to the foil is required to initiate the air gap, and once this has been achieved, no wear occurs. Unlike aero or hydrostatic bearings, foil bearings require no external pressurization system for the working fluid, so the hydrodynamic bearing is self-starting.

Unlike contact-roller bearings, an air bearing (or air caster) utilizes a thin film of pressurized air to provide an exceedingly low friction load-bearing interface between surfaces. The two surfaces don't touch. Being non-contact, air bearings avoid the traditional bearing-related problems of friction, wear, particulates, and lubricant handling, and offer distinct advantages in precision positioning, such as lacking backlash and stiction, as well as in high-speed applications.

The air cooling feature of the centrifugal compressor 10 will now be discussed with reference to FIG. 4. The centrifugal compressor 10 incorporates four (4) separate air passageways, or circuits:

-   -   1) Compressor Air passageway 120—also known as “process air”         that enters through the compressor air inlet 15 and exits at the         volute exit 85. This air is used for any number of applications,         ranging from aircraft to automotive to industrial applications.     -   2) Secondary Air Bleed passageway 125—This air ‘bleeds’ past the         impeller 90 periphery and flows though a first air bearing         journal 80, then the electric motor 95, past the second air         bearing journal 80, then against the forward thrust bearing pad         element 115, and then exits into the heat sink area (shown in         FIG. 3). Exit ports 130 for the air are provided in the rear         cover 65 (shown in FIG. 6).     -   3) Cooling Air passageway 135—This air is supplied by the         rear-mounted cooling fan 105 which draws air from the cool         ambient environment. Air is forced through and around the heat         sink fins 50 in the finned heat exchanger 45 (shown in FIG. 3)         that have a large surface area and high convective heat         transfer. A low pressure region is created by the cooling air         flow passing over the exit ports 130 of the rear cover 65, at         the point where secondary air bleed flow enters the heat sink.         This further enhances secondary air flow through the bearing and         motor system, hence improving cooling efficiency. The         aft-mounted cooling fan 105 is directly coupled to the         high-speed impeller shaft 92. This fan is sized to provide on         the order of 35 cubic feet per minute (“CFM”) of airflow at only         a moderate pressure rise.     -   4) Tertiary Air Bleed passageway 140—The fourth air circuit is         an additional air-bleed which is obtained from the periphery of         the cooling fan 105 (i.e., bled off), and is directed against         the aft section of the thrust bearing surface 70. This bleed air         exits into the heat sink cooling fins 50. Tertiary air bleed         flow is also enhanced by the same low pressure region at the         exit ports 130 of rear cover 65.

By including four (4) distinct air passageways the centrifugal compressor 10 can be compact yet extremely efficient. For example, the highly effective heat sink fin 50 arrangement is designed to reject 1 kilowatt (“kW”) of heat or more, resulting in only a moderate temperature rise of the supplied cooling air. In one example, the electric motor total thermal losses of 900 watts will result in cooling air discharged at approximately 100° C., with the cooling air inlet at approximately 45° C. This data relates to a sustained, full load, high-speed, thermally stabilized operating condition. Parasitic power loss operates the cooling fan, but this amount on the order of 75 Watts of shaft power, or 0.5% of the maximum 15 kW power rating of the centrifugal compressor 10.

Referring now to FIGS. 5-6, a second embodiment centrifugal compressor 10 that includes water cooling in addition to air cooling is illustrated. The housing 30 includes a cooling inlet 145 and cooling outlet 150 for circulating a liquid cooling medium through a liquid heat exchanger 155. In this embodiment, the finned heat exchanger 45, shown in FIG. 3, is replaced with a liquid heat exchanger 155 that includes the liquid inlet 150 and outlet 145. The four air passageways described above are still included, but instead of passing through the fin elements 50, the air, after flowing through the passageways described above, exits the air exit ports 130 in the rear cover 65.

Not illustrated is an electronic module. The electronic module controls the centrifugal compressor 10 through use of a Hall effect sensor, software and other elements as required. For example, the electronic module may include computer hardware and software and may include a computer program product which is embodied on one or more computer-usable storage media having computer-usable program code embodied therein. Computer program instructions may also be stored in a computer-readable memory that can direct the centrifugal compressor 10 to function in a particular manner, such that the instructions stored in the computer-readable memory produce an operating cycle.

Thus, it is seen that a centrifugal compressor is provided. One skilled in the art will appreciate that the present invention can be practiced by other than the above-described embodiments, which are presented in this description for purposes of illustration and not of limitation. The specification and drawings are not intended to limit the exclusionary scope of this patent document. It is noted that various equivalents for the particular embodiments discussed in this description may practice the invention as well. That is, while the present invention has been described in conjunction with specific embodiments, it is evident that many alternatives, modifications, permutations and variations will become apparent to those of ordinary skill in the art in light of the foregoing description. Accordingly, it is intended that the present invention embrace all such alternatives, modifications and variations as fall within the scope of the appended claims. The fact that a product, process or method exhibits differences from one or more of the above-described exemplary embodiments does not mean that the product or process is outside the scope (literal scope and/or other legally-recognized scope) of the following claims. 

1. An apparatus, comprising: a compressor housing; a rotatable assembly mounted for rotation about an axis within the housing, and comprising an impeller forming part of a compressor stage within the housing and a motor rotor forming an armature of a motor for driving the rotating assembly about the axis; a first air intake located at a first end of the apparatus, the first air intake providing an air source for the compressor stage; and a second air intake located at a second end of the apparatus, the second air intake providing an air source for at least two air cooling passageways.
 2. The apparatus of claim 1, further comprising a fan attached to the rotatable assembly, the fan mounted within the second air intake, at a distal end opposite from the impeller.
 3. The apparatus of claim 1, where the at least two air cooling passageways begin at the second air intake, and proceed toward the first air intake.
 4. The apparatus of claim 1, further comprising a heat exchanger located about a portion of the rotatable assembly, the heat exchanger comprising a plurality of fin elements.
 5. The apparatus of claim 1, further comprising a cover element coupled to the compressor housing, the cover element including the second air intake and a plurality of apertures sized to allow air to escape from at least one exit of the at least two air cooling passageways.
 6. The apparatus of claim 1, further comprising a liquid heat exchanger located about a portion of the rotatable assembly, the liquid heat exchanger having a liquid fluid inlet and a liquid fluid outlet.
 7. The apparatus of claim 6, where the at least two air cooling passageways begin at the second air intake, and proceed toward the first air intake and air exiting the at least two air cooling passageways exits through a plurality of apertures sized to allow air to escape from at least one exit of the at least two air cooling passageways.
 8. The apparatus of claim 1, where rotatable assembly comprises a shaft that is supported by at least two air bearings.
 9. An apparatus, comprising: a compressor housing; a rotatable assembly mounted for rotation about an axis within the housing, and comprising an impeller forming part of a compressor stage within the housing and a motor rotor forming an armature of a motor for driving the rotating assembly about the axis; a first air passageway located within the housing, the first air passageway comprising an airflow passageway to direct air from the first end toward the second end; and a second air passageway located within the housing, the second air passageway comprising an airflow passageway to direct air from the second end toward the first end.
 10. The apparatus of claim 9, where the first air passageway allows air to enter through a compressor air inlet, through the compressor stage and exit through a volute exit.
 11. The apparatus of claim 9, further comprising an impeller air passageway that is structured to allow air to flow past the impeller and through a first and second air bearing journal and then into a heat exchanger element.
 12. The apparatus of claim 9, further comprising a fan attached to the rotatable assembly, the fan mounted within a second air intake, at a distal end opposite from the impeller
 13. The apparatus of claim 12, where the second air passageway begins at the second air intake and comprises an air passage that directs air through a plurality fin elements located within a heat exchanger element that is located about a portion of the rotatable assembly.
 14. The apparatus of claim 12, where the second air passageway begins at the second air intake and comprises an air passage that directs air against a section of the rotatable assembly and then through a plurality fin elements located within a heat exchanger element that is located about a portion of the rotatable assembly.
 15. The apparatus of claim 9, further comprising a liquid heat exchanger located about a portion of the rotatable assembly, the liquid heat exchanger having a liquid fluid inlet and a liquid fluid outlet.
 16. The apparatus of claim 9, where rotatable assembly comprises a shaft that is supported by at least two air bearings.
 17. An apparatus, comprising: a compressor housing; a rotatable assembly mounted for rotation about an axis within the housing, and comprising an impeller forming part of a compressor stage within the housing and a motor rotor forming an armature of a motor for driving the rotating assembly about the axis; a first air passageway located at a first end of the apparatus, the first air passageway enabling air to enter through a compressor air inlet, through the compressor stage and exit through a volute exit; a second air passageway having an aperture within the compressor stage, and enabling air to flow past the impeller and through a first and second air bearing journal and then into a heat exchanger element located about a portion of the rotatable assembly; a third air passageway beginning at a second air intake distal from the compressor air inlet, the third air passageway comprising an air passage that directs air into the heat exchanger element; and a fourth air passageway beginning at the second air intake and comprising an air passage that directs air against a section of the rotatable assembly and then into heat exchanger element.
 18. The apparatus of claim 17, further comprising a fan attached to the rotatable assembly, the fan mounted within the second air intake.
 19. The apparatus of claim 17, where the heat exchanger comprises a plurality fin elements.
 20. The apparatus of claim 17, further comprising a cover element coupled to the compressor housing, the cover element including the second air intake and a plurality of apertures sized to allow air to escape from the heat exchanger. 